The H Beta Index as an Age Indicator of Old Stellar Systems: The Effects of Horizontal-Branch Stars

The strength of the H$\beta$ index has been computed for the integrated spectra of model globular clusters from the evolutionary population synthesis. These models take into account, for the first time, the detailed systematic variation of horizontal-branch (HB) morphology with age and metallicity. Our models show that the H$\beta$ index is significantly affected by the presence of blue HB stars. Because of the contribution from blue HB stars, the H$\beta$ does not monotonically decrease as metallicity increases at a given age. Instead, it reaches a maximum strength when the distribution of HB stars is centered around 9500 K, the temperature where the H$\beta$ index becomes strongest. Our models indicate that the strength of the H$\beta$ index increases as much as 0.75 {\AA} due to the presence of blue HB stars. The comparison of the recent Keck observations of the globular cluster system in the Milky Way Galaxy with those in giant elliptical galaxies, NGC 1399 and M87, shows a systematic shift in the H$\beta$ against metallicity plane. Our models suggest that this systematic difference is understood if the globular cluster systems in giant elliptical galaxies are several billion years older, in the mean, than the Galactic counterpart. Further observations of globular cluster systems in the external galaxies from the large ground-based telescopes and space UV facilities will enable to clarify whether this difference is indeed due to the age difference or other explanations are also possible.Comment: 21 pages, 8 figures, Accepted for publication in the Astronomical Journal, August 2000 issue, Postscript files are available at http://csaweb.yonsei.ac.kr/~hclee/Hbet

In utero exposure to Δ9‐tetrahydrocannabinol leads to postnatal catch‐up growth and dysmetabolism in the adult rat liver

The rates of gestational cannabis use have increased despite limited evidence for its safety in fetal life. Recent animal studies demonstrate that prenatal exposure to Δ9‐tetrahydrocannabinol (Δ9‐THC, the psychoactive component of cannabis) promotes intrauterine growth restriction (IUGR), culminating in postnatal metabolic deficits. Given IUGR is associated with impaired hepatic function, we hypothesized that Δ9‐THC offspring would exhibit hepatic dyslipidemia. Pregnant Wistar rat dams received daily injections of vehicular control or 3 mg/kg Δ9‐THC i.p. from embry-onic day (E) 6.5 through E22. Exposure to Δ9‐THC decreased the liver to body weight ratio at birth, followed by catch‐up growth by three weeks of age. At six months, Δ9‐THC‐exposed male offspring exhibited increased visceral adiposity and higher hepatic triglycerides. This was instigated by augmented expression of enzymes involved in triglyceride synthesis (ACCα, SCD, FABP1, and DGAT2) at three weeks. Furthermore, the expression of hepatic DGAT1/DGAT2 was sustained at six months, concomitant with mitochondrial dysfunction (i.e., elevated p66shc) and oxidative stress. Interest-ingly, decreases in miR‐203a‐3p and miR‐29a/b/c, both implicated in dyslipidemia, were also observed in these Δ9‐THC‐exposed offspring. Collectively, these findings indicate that prenatal Δ9‐ THC exposure results in long‐term dyslipidemia associated with enhanced hepatic lipogenesis. This is attributed by mitochondrial dysfunction and epigenetic mechanisms

Implementation of a new urban energy budget scheme in the MetUM. Part I: Description and idealized simulations

This paper describes the formulation of a new urban scheme, MORUSES (Met Office–Reading Urban Surface Exchange Scheme) for use in the Met Office Unified Model. The implementation of the new scheme ensures that (1) the new scheme offers more flexibility in the parametrization of the building properties, and hence provides a more realistic representation of the fluxes; (2) the bulk outputs are in satisfactory agreement with previous observational studies; and (3) the impact of the new scheme on the energy balance fluxes is similar to the impact of the current urban scheme when set up to mimic it. As well as having a better physical basis, MORUSES also gains in flexibility in applications and adaptations to different urban materials as well as urban planning. The new scheme represents the urban area as a composition of two tiles, a canyon and a roof, using a simple 2D geometry. Sensitivity analysis to canyon geometry and thickness of the roof canopy emphasizes the gain in flexibility captured by the new scheme. Copyright © 2010 Royal Meteorological Society and Crown Copyrigh

Survey of H-alpha emission from thirty nearby dwarf galaxies

Measurements of the H-alpha flux from 30 neighboring dwarf galaxies are presented. After correction for absorption, these fluxes are used to estimate the star formation rate (SFR). The SFR for 18 of the galaxies according to the H-alpha emission are compared with estimates of the SFR from FUV magnitudes obtained with the GALEX telescope. These are in good agreement over the range log[SFR] = [-3,0]M sun/yr.Comment: 18 pages, 10 figures, 3 table

The North Ecliptic Pole Wide survey of AKARI: a near- and mid-infrared source catalog

We present a photometric catalog of infrared (IR) sources based on the North Ecliptic PoleWide field (NEP-Wide) survey of AKARI, which is an infrared space telescope launched by Japan. The NEP-Wide survey covered 5.4 deg2 area, a nearly circular shape centered on the North Ecliptic Pole, using nine photometric filter-bands from 2 - 25 {\mu}m of the Infrared Camera (IRC). Extensive efforts were made to reduce possible false objects due to cosmic ray hits, multiplexer bleeding phenomena around bright sources, and other artifacts. The number of detected sources varied depending on the filter band: with about 109,000 sources being cataloged in the near-IR bands at 2 - 5 {\mu}m, about 20,000 sources in the shorter parts of the mid-IR bands between 7 - 11 {\mu}m, and about 16,000 sources in the longer parts of the mid-IR bands, with \sim 4,000 sources at 24 {\mu}m. The estimated 5? detection limits are approximately 21 magnitude (mag) in the 2 - 5 {\mu}m bands, 19.5 - 19 mag in the 7 - 11 {\mu}m, and 18.8 - 18.5 mag in the 15 - 24 {\mu}m bands in the AB magnitude scale. The completenesses for those bands were evaluated as a function of magnitude: the 50% completeness limits are about 19.8 mag at 3 {\mu}m, 18.6 mag at 9 {\mu}m, and 18 mag at 18 {\mu}m band, respectively. To construct a reliable source catalog, all of the detected sources were examined by matching them with those in other wavelength data, including optical and ground-based near-IR bands. The final band-merged catalog contains about 114,800 sources detected in the IRC filter bands. The properties of the sources are presented in terms of the distributions in various color-color diagrams.Comment: Accepted for publication in A&A, 23 pages, 27 figure

Diverging UV and Halpha fluxes of star forming galaxies predicted by the IGIMF theory

Although the stellar initial mass function (IMF) has only been directly determined in star clusters it has been manifoldly applied on galaxy-wide scales. But taking the clustered nature of star formation into account the galaxy-wide IMF is constructed by adding all IMFs of all young star clusters leading to an integrated galactic initial mass function (IGIMF). The IGIMF is top-light compared to the canonical IMF in star clusters and steepens with decreasing total star formation rate (SFR). This discrepancy is marginal for large disk galaxies but becomes significant for SMC-type galaxies and less massive ones. We here construct IGIMF-based relations between the total FUV and NUV luminosities of galaxies and the underlying SFR. We make the prediction that the Halpha luminosity of star forming dwarf galaxies decreases faster with decreasing SFR than the UV luminosity. This turn-down of the Halpha-UV flux ratio should be evident below total SFRs of 10^-2 M_sun/yr.Comment: accepted by MNRA

Spatial Clustering of High Redshift Lyman Break Galaxies

We present a physically motivated semi-analytic model to understand the clustering of high redshift LBGs. We show that the model parameters constrained by the observed luminosity function, can be used to predict large scale (\theta > 80 arcsec) bias and angular correlation function of galaxies. These predictions are shown to reproduce the observations remarkably well. We then adopt these model parameters to calculate the halo occupation distribution (HOD) using the conditional mass function. The halo model using this HOD is shown to provide a reasonably good fit to the observed clustering of LBGs at both large (\theta>80") and small (\theta < 10") angular scales for z=3-5 and several limiting magnitudes. However, our models underpredict the clustering amplitude at intermediate angular scales, where quasi-linear effects are important. The average mass of halos contributing to the observed clustering is found to be 6.2 x 10^{11} M_\odot and the characteristic mass of a parent halo hosting satellite galaxies is 1.2 \times 10^{12} M_\odot for a limiting absolute magnitude of -20.5 at z=4. For a given threshold luminosity these masses decrease with increasing z and at any given z these are found to increase with increasing value of threshold luminosity. We find that approximately 40 % of the halos above a minimum mass M_{min}, can host detectable central galaxies and about 5-10 % of these halos are likely to also host a detectable satellite. The satellites form typically a dynamical timescale prior to the formation of the parent halo. The small angular scale clustering is due to central-satellite pairs and is quite sensitive to changes in the duration of star formation in a halo. The present data favor star formation in a halo lasting typically for a few dynamical time-scales. Our models also reproduce different known trends between parameters related to star formation.Comment: Accepted for publication in MNRA

Photometric redshift accuracy in AKARI Deep Surveys

We investigate the photometric redshift accuracy achievable with the AKARI infrared data in deep multi-band surveys, such as in the North Ecliptic Pole field. We demonstrate that the passage of redshifted policyclic aromatic hydrocarbons and silicate features into the mid-infrared wavelength window covered by AKARI is a valuable means to recover the redshifts of starburst galaxies. To this end we have collected a sample of ~60 galaxies drawn from the GOODS-North Field with spectroscopic redshift 0.5<~z_spec<~1.5 and photometry from 3.6 to 24 micron, provided by the Spitzer, ISO and AKARI satellites. The infrared spectra are fitted using synthetic galaxy Spectral Energy Distributions which account for starburst and active nuclei emission. For ~90% of the sources in our sample the redshift is recovered with an accuracy |z_phot-z_spec|/(1+z_spec)<~10%. A similar analysis performed on different sets of simulated spectra shows that the AKARI infrared data alone can provide photometric redshifts accurate to |z_phot-z_spec|/(1+z_spec)<~10% (1-sigma) at z<~2. At higher redshifts the PAH features are shifted outside the wavelength range covered by AKARI and the photo-z estimates rely on the less prominent 1.6 micron stellar bump; the accuracy achievable in this case on (1+z) is ~10-15%, provided that the AGN contribution to the infrared emission is subdominant. Our technique is no more prone to redshift aliasing than optical-uv photo-z, and it may be possible to reduce this aliasing further with the addition of submillimetre and/or radio data.Comment: 27 pages, 12 figures, 4 tables. Accepted for publication on MNRA

New abundance measurements in UKS 1927-177, a very metal-poor galaxy in the Local Group

We present new results from optical spectroscopy of the brightest Hii region in the dwarf irregular galaxy UKS 1927-177 in Sagittarius (SagDIG). From high signal-to-noise spectra, reddening-corrected line flux ratios have been measured with typical uncertainties of a few percent, from which the oxygen abundance is rediscussed, and new abundance estimates are derived for N and Ne. The O abundance in SagDIG, estimated with the empirical abundance indicator R23 and other methods, is in the range 12+log(O/H)=7.26 to 7.50. The fact that SagDIG is ~10 times closer than IZw18 makes it an ideal target to test the hypothesis of the existence of young galaxies in the present-day universe. Indeed, stellar photometry suggests that this galaxy may harbor a stellar population older than a few Gyr, and possibly an old stellar component as well. The case of SagDIG therefore supports the view that very low chemical abundances can be maintained throughout the life of a dwarf stellar system, even in the presence of multiple star formation episodes.Comment: 6 pages, 3 figures, accepted for publication in A&A, main journa